Poly(ethylene terephthalate) (“2GT”) and poly(butylene terephthalate) (“4GT”), generally referred to as “polyalkylene terephthalates”, are common commercial polyesters. Polyalkylene terephthalates have excellent physical and chemical properties, in particular chemical, heat and light stability, high melting points and high strength. As a result they have been widely used for resins, films and fibers.
Poly(trimethylene terephthalate) (“3GT”) has achieved growing commercial interest as a fiber because of the recent developments in lower cost routes to 1,3-propane diol (PDO), one of the polymer backbone monomer components. 3GT has long been desirable in fiber form for its disperse dyeability at atmospheric pressure, low bending modulus, elastic recovery and resilience.
Spinning and drawing the 3GT filament may be carried out continuously in a single combined operation. The yarn produced by such a process may be referred to as spin-draw yarn (SDY). However the yarn so produced has a tendency to shrink on the tube on which it is wound, causing a heavy bulge in the yarn package, or even crushing the tube. This problem is more severe when larger packages of yarn are made, such as packages containing more than about 4 kg of yarn, and when the spinning speed is greater than about 3500 m/min. As a result of tube crushing, the yarn packages are stuck on the spindles on the winder, and can not be readily removed. In some embodiments, e.g., in some multifilament yarns, the yarn has an IV from about 0.7 to about 1.1.
Several solutions have been proposed. For example, when winding a small package, the shrinkage force can be reduced, because much fewer yarn layers are wound on the tube. However, packaging with small packages becomes uneconomical. The use of a thicker and stronger tube creates an unacceptably heavy package even when the package size is small, and is inadequate in strength when the package size is large.
It is also well known that the use of a slow spinning speed in a spin-draw process minimizes this problem, and improves the bulge or windup tube crushing. When a low spinning speed is applied, the low speed allows a high overfeed between the draw roll and windup in a two godet process, or a high overfeed between the second and third godet in a three godet process. Together with the large overfeed, the low speed allows more time to relax the filaments during spinning. However, the low spinning speed results in low productivity and the process becomes uneconomical.
Japanese Kokai JP 9339502 discloses a spin-draw process for 3GT in which the extruded fiber is wound on a first roller at 300-3500 m/min. and 30-60° C., stretched to 1.3 to 4 times its length through a second roller at 100-160° C., and then wound and cooled on a third roller. However, this technology could not make packages with a weight of more than 2 kg, as pointed out in subsequent patent JP 99302919.
U.S. Pat. No. 6,284,370 discloses a spin-draw process for 3GT so as to obtain a cheese-like package. The molten multifilament enters a holdup zone at 30-200° C. to solidify the filaments. It then passes the first godet which is heated at 30-80° C. at a speed of 300-3500 m/min, is drawn at a draw ratio of 1.3-4 to a second godet at 100-160° C., before being wound into a package at a slower winding speed. The winding tension is preferably between 0.05 and 0.4 gram/denier. In two examples (Examples 11 and 12), the filaments are cooled on a third godet. Neither example shows a high spinning speed in combination with a suitable third godet overfeed. Package sizes ranged from 1 to 5 kg.
Japanese Kokai JP 99302919, by co-applicants to U.S. Pat. No. 6,284,370, discloses a similar process. After the molten 3GT multifilament is extruded and solidified as before, it passes the first godet which is heated at 40-70° C. at a speed of 300-3000 m/min, is drawn at a draw ratio of 1.5-3 to a second godet at 120-160° C., and is cooled down before being wound into a package at a slower winding speed. This final cooling was done by cooling on a third godet (Example 1), or by applying cold water (Example 3). The second and third godets were run at the same speed, i.e., with no third godet overfeed. The winding tension, although important, was not disclosed. Package sizes were up to 6 kg.
The above processes are limited in package size and winding speed. There is a need for a spin-draw process which enables spinning 3GT fibers at a speed of 4000 m/min or more at the second godet into a cheese-like package containing over 6 kg of fiber.